U.S. patent application number 11/750682 was filed with the patent office on 2008-11-20 for optical panel for front projection under ambient lighting conditions.
This patent application is currently assigned to FUJIFILM MANUFACTURING U.S.A. INC.. Invention is credited to Chuan Lee, Kimiaki Miyamoto, Richard S. Sarvas, James F. Shanley, Kenneth L. Strickland, Benjamin M. Wicker.
Application Number | 20080285125 11/750682 |
Document ID | / |
Family ID | 39671427 |
Filed Date | 2008-11-20 |
United States Patent
Application |
20080285125 |
Kind Code |
A1 |
Lee; Chuan ; et al. |
November 20, 2008 |
OPTICAL PANEL FOR FRONT PROJECTION UNDER AMBIENT LIGHTING
CONDITIONS
Abstract
An optical display panel that comprises a plurality of stacked
optical waveguides including a plurality of stacked optical
waveguides each having an optical core with a first and a second
surface, a cladding layer on each of the first and second surfaces
of the core, a diffuser on the front face of the stacked
waveguides, and a reflector on the back face of the stacked
waveguides. The stacked waveguides form a front face and a back
face and images are viewed from the front face of the stacked
waveguides, which are planar.
Inventors: |
Lee; Chuan; (Greer, SC)
; Strickland; Kenneth L.; (Simpsonville, SC) ;
Wicker; Benjamin M.; (Ware Shoals, SC) ; Miyamoto;
Kimiaki; (Greenwood, SC) ; Shanley; James F.;
(Westborough, MA) ; Sarvas; Richard S.;
(Huntington, WV) |
Correspondence
Address: |
THOMPSON HINE L.L.P.;Intellectual Property Group
P.O. BOX 8801
DAYTON
OH
45401-8801
US
|
Assignee: |
FUJIFILM MANUFACTURING U.S.A.
INC.
Greenwood
SC
Scram Technologies, Inc.
Bowie
MD
|
Family ID: |
39671427 |
Appl. No.: |
11/750682 |
Filed: |
May 18, 2007 |
Current U.S.
Class: |
359/449 |
Current CPC
Class: |
G02B 6/08 20130101; G03B
21/60 20130101 |
Class at
Publication: |
359/449 |
International
Class: |
G03B 21/56 20060101
G03B021/56 |
Claims
1. An optical display panel for a front projection screen, the
optical panel comprising: a plurality of stacked optical
waveguides, each stacked waveguide including an optical core having
a first and a second surface, a cladding layer on each of the first
and second surfaces of the core, wherein the stacked waveguides
form a front face and a back face at opposite ends of the stacked
waveguides, and wherein images are viewed from the front face of
the stacked wave guides; a diffuser on the front face of the
stacked waveguides; and a reflector on the back face of the stacked
waveguides; wherein each of the stacked waveguides is planar.
2. The optical display panel of claim 1 wherein the reflector is a
reflective material or reflective substrate, wherein the reflective
material or reflective substrate is comprised of a material
selected from the group consisting of aluminum or aluminum
compounds, silver or silver compounds, titanium or titanium
compounds, gold or gold compounds, mercury or mercury compounds,
barium or barium compounds, stainless steel, and mixtures or
combinations thereof.
3. The optical display panel of claim 2 wherein the reflector is a
metallized film.
4. The optical display panel of claim 3 wherein the metallized film
is laminated onto the back face of the stacked waveguides.
5. The optical display panel of claim 2 wherein the reflector is
deposited on the back face by vapor deposition or is painted
thereon.
6. The optical display panel of claim 1 wherein the diffuser is
laminated onto the front face.
7. The optical display panel of claim 1 wherein the diffuser has at
least one of an anti-glare or an abrasion-resistant film or coating
thereon.
8. The optical display panel of claim 1 wherein the core includes
at least one of glass, a polycarbonate, a polymethylmethacrylate, a
polycyclic olefin, a polyester, a cellulose, or copolymers
thereof.
9. The optical display panel of claim 1 wherein the core has a
first refractive index and the cladding layers have a second
refractive index, the second refractive index is less than the
first refractive index.
10. The optical display panel of claim 9 wherein the core is
polycarbonate with a refractive index of about 1.58 and the
cladding layers have a refractive index less than about 1.58.
11. The optical display panel of claim 1 wherein the cladding layer
includes a light absorbing material.
12. The optical display panel of claim 11 wherein the light
absorbing material includes at least one of a carbon black
material, a pigment, a dye, or combinations thereof.
13. The optical display panel of claim 1 further comprising a first
light absorbing layer applied to the cladding layer that is on the
first surface of the optical core and a second light absorbing
layer applied to the cladding layer that is on the second surface
of the optical core.
14. The optical display panel of claim 13 wherein the light
absorbing layer includes a light absorbing material and an
adhesive.
15. The optical display panel of claim 1 further comprising an
adhesive layer between the cladding layers on consecutively stacked
waveguides.
16. The optical display panel of claim 13 further comprising an
adhesive layer between the first light absorbing layer and the
second light absorbing layer on consecutively stacked
waveguides.
17. The optical display panel of claim 1 wherein a dichroic filter
is provided between the back face and the reflector, wherein the
dichroic filter passes substantially only wavelengths of light
corresponding to projected image light forming the images.
18. The optical display of claim 1 wherein the reflector is a
dichroic mirror.
19. The optical display of claim 18 wherein the a polarized film is
provided between the back face and the dichroic mirror.
20. An optical display panel for a front projection screen, the
optical panel comprising: a plurality of stacked optical
waveguides, each stacked waveguide including an optical core having
a first and a second surface, a cladding layer on each of the first
and second surfaces of the core, wherein the stacked waveguides
form a front face and a back face at opposite ends of the stacked
waveguides, and wherein images are viewed from the front face of
the stacked wave guides; a front diffuser on the front face of the
stacked waveguides; a back diffuser on the back face of the stacked
waveguides; and a reflector behind the back diffuser on a face of
the back diffuser opposite the back face; wherein each of the
stacked waveguides is planar.
21. The optical display panel of claim 20 wherein the reflector is
a reflective material or reflective substrate, wherein the
reflective material or reflective substrate is comprised of a
material selected from the group consisting of aluminum or aluminum
compounds, silver or silver compounds, titanium or titanium
compounds, gold or gold compounds, mercury or mercury compounds,
barium or barium compounds, stainless steel, and mixtures or
combinations thereof.
22. The optical display panel of claim 21 wherein the reflector is
a metallized film.
23. The optical display panel of claim 22 wherein the back diffuser
is laminated between the metallized film and the back face of the
waveguides.
24. The optical display panel of claim 23 wherein the back diffuser
is applied to the back face of the stacked waveguides and the
reflector is deposited on the back diffuser by vapor deposition or
is painted thereon.
25. The optical display panel of claim 20 wherein the front
diffuser is laminated onto the front face of the stacked
waveguides.
26. The optical display panel of claim 20 wherein the front
diffuser has at least one of an anti-glare or an abrasion-resistant
film or coating thereon.
27. The optical display panel of claim 20 wherein the core includes
at least one of glass, a polycarbonate, a polymethylmethacrylate, a
polycyclic olefin, a polyester, a cellulose, or copolymers
thereof.
28. The optical display panel of claim 20 wherein the core has a
first refractive index and the cladding layers have a second
refractive index, the second refractive index is less than the
first refractive index.
29. The optical display panel of claim 20 wherein the cladding
layers include a light absorbing material.
30. The optical display panel of claim 29 wherein the light
absorbing material includes at least one of a carbon black
material, a pigment, a dye, or combination thereof.
31. The optical display panel of claim 20 further comprising a
first light absorbing layer applied to the cladding layer that is
on the first surface of the optical core and a second light
absorbing layer applied to the cladding layer that is on the second
surface of the optical core.
32. The optical display panel of claim 31 wherein the light
absorbing layer includes a light absorbing material and an
adhesive.
33. The optical display panel of claim 20 further comprising an
adhesive layer between the cladding layers on consecutively stacked
waveguides.
34. The optical display panel of claim 31 further comprising an
adhesive layer between the first light absorbing layer and the
second light absorbing layer on consecutively stacked
waveguides.
35. The optical display panel of claim 20 wherein a dichroic filter
is provided between the back face and the back diffuser, wherein
the dichroic filter passes substantially only wavelengths of light
corresponding to projected image light forming the images.
36. The optical display panel of claim 20 wherein a dichroic filter
is provided between the back diffuser and the reflector, wherein
the dichroic filter passes substantially only wavelengths of light
corresponding to projected image light forming the images.
37. The optical display of claim 20 wherein the reflector is a
dichroic mirror.
38. The optical display of claim 37 wherein the a polarized film is
provided between the back face and the dichroic mirror.
Description
BACKGROUND
[0001] The present application relates generally to an optical
panel for use as a front projection screen.
[0002] Optical waveguides have been used to develop front
projection optical display screens as taught in U.S. Pat. Nos.
7,116,873, 6,741,779, and 6,535,674 to Veligdan, which are
incorporated herein by reference. The waveguides disclosed include
a central core disposed between cladding layers where the index of
refraction of the cladding is less than the index of refraction for
the core. The wave guides are stacked together and secured to form
the projection screen. Each waveguide may include a black layer
disposed in or between the cladding layers on the adjacent
waveguides. The faces on one end of the plurality of stacked
waveguides form an outlet face at one end and a back face at the
opposite end. A reflector that reflects light within the waveguides
is connected to the back face. Light enters the front outlet faces
of the waveguides and is internally reflected to the back face
where it strikes the reflector and is reflected back within the
waveguides and for projection from the front or outlet face of the
display screen.
[0003] Ambient light often interferes with the projected image on
many conventional screens such that the image has low brightness,
low contrast, and high glare under ambient conditions. To view the
image, the lights in the room are either turned off or dimmed,
and/or light coming in from outside the room is shielded. Another
problem found in front projection screens is the presence of a
reflective hot spot. A reflective hot spot is an area or spot which
gives unusual high reflective bright light across the screen
surface. The hot spot may be an enlarged and/or greatly blurred
reflection of bright light. The unusual brightness of the hot spot
may obstruct the view of the image by distorting the contrast with
portion of the image surrounding the hot spot. The viewer may be
"blinded" by the hot spot such that the rest of the image appears
blurry. Therefore, there is a need for an optical panel that has
good screen properties (e.g. high brightness, high contrast, low
glare, and no hot spot) under ambient room conditions or any other
various lighting conditions without the need to alter the lighting
conditions of the surroundings.
SUMMARY
[0004] In one embodiment, disclosed herein an optical display panel
comprises a plurality of stacked optical waveguides. Each stacked
waveguide is planar, has a front face and a back face at opposite
ends of the stacked waveguides, and includes an optical core having
a first and a second surface, a cladding layer on each of the first
and second surfaces of the core, a diffuser on the front face of
the stacked waveguides, and a reflector on the back face of the
stacked waveguides. Images are viewed from the front face of the
stacked waveguides. Generally the waveguides have a thin
rectangular cross-section.
[0005] Another embodiment of an optical display panel comprises a
plurality of stacked waveguides. Each stacked waveguide is planar,
has a front face and a back face at opposite ends of the stacked
waveguides, and includes an optical core having a first and a
second surface, a cladding layer on each face of the first and
second surfaces of the core, a front diffuser on the front face of
the stacked waveguides, a back diffuser on the back face of the
stacked waveguide, and a reflector behind the back diffuser on the
face of the diffuser opposite the waveguide. Images are viewed from
the front face of the stacked waveguides.
[0006] Other aspects of the disclosed optical waveguides and
associated methods will become apparent from the following
description, the accompanying drawings and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a side elevational view of a waveguide showing the
acceptance angle;
[0008] FIGS. 2 and 3 are side elevational views of embodiments of
an optical panel;
[0009] FIGS. 4-10 are side elevational views of various embodiment
of waveguides; and
[0010] FIG. 11 is a side elevational view of one embodiment of an
optical panel including a dichroic filter.
DETAILED DESCRIPTION
[0011] It is to be understood that the figures and descriptions of
the present invention may have been simplified to illustrate
elements that are relevant for a clear understanding of the present
invention, while eliminating, for purposes of clarity, other
elements found in a typical projection system. Those of ordinary
skill in the art will recognize that other elements may be
desirable and/or required in order to implement the present
invention. However, because such elements are well known in the
art, and because they do not facilitate a better understanding of
the present invention, a discussion of such elements is not
provided herein. It is also to be understood that the drawings
included herewith only provide diagrammatic representations of
structures of the present invention and that structures falling
within the scope of the present invention may include structures
different than those shown in the drawings. Reference will now be
made to the drawings wherein like structures are provided with like
reference designations.
[0012] As used herein the term "waveguide" means a device for
guiding the flow of electromagnetic waves along a desired path.
Waveguides include a core material bounded by a cladding wherein
the index of refraction of the cladding is less than the index of
refraction of the core. The waveguide may further include a light
absorbing layer and/or an adhesive to adhere a plurality of
waveguides together.
[0013] In simple terms, the behavior of light entering the core
material in a waveguide is fundamentally controlled by the property
of the core, cladding, any other layers if included, and the medium
surrounding the waveguide. As illustrated in FIG. 1, a light ray
entering waveguide 8 at core 12 having an axis 17 is either
refracted into the cladding 18A, 18B and attenuated (absorbed), or
it is totally internally reflected at the core/cladding boundary.
Total internal reflection is the reflection of the total amount of
incident light at the boundary between the core and cladding. In
this manner light travels within the core along the length of the
waveguide. The maximum angle at which the light ray may enter core
12 and travel by total internal reflection within the core is
termed the acceptance angle A. The value of the acceptance angle
depends mainly on the properties, including the refractive index,
of the selected core and cladding. The acceptance angle A is
measured between the incident ray and the normal line N to the
front face 21 of core 12 and may be positive or negative. The
larger the difference in refractive index between core 12 and the
cladding 18A, 18B, the larger the acceptance angle may be for light
rays entering core 12 to be totally internally reflected.
[0014] As used herein the term "panel" means a plurality of
waveguides stacked and secured to one another such that the panel
may be used for viewing images. The panel may be part of a screen
used in visual projection applications.
[0015] As shown in FIG. 2, one embodiment of a panel 20 includes a
plurality of stacked optical waveguides 8, wherein the stacked
optical waveguides 8 form a front face 21 and a back face 22 at
opposing ends of the stacked waveguides 8. A diffuser 24 is on the
front face 21 of the stacked waveguides 8. A reflector 29 is on
back face 22 of the stacked waveguides 8. Reflector 29 may be a
reflective material or reflective substrate as described in more
detail below. In one embodiment, the waveguides 8 may be in the
form of planar sheets or ribbons. The waveguides 8 include an
optical core 12 and at least one cladding layer 18 that may include
a light absorbing material. In other embodiment, cladding layer 18
may be clear and a separate light absorbing layer may be applied to
the cladding layers between adjacent waveguides 8. In another
embodiment, as shown in FIG. 3, panel 20 may include a front
diffuser 24A and a back diffuser 24B. In one embodiment, back
diffuser 24B may be between the back face 22 of the stacked
waveguides 8 and the reflector 29. In another embodiment, back
diffuser 24B may be part of the reflector 29.
[0016] FIGS. 4-10 show various embodiments of waveguides, generally
designated 8. The waveguides 8, as shown in FIG. 4, include an
optical core 12 having a first surface 14 and a second surface 16,
a first cladding layer 18A applied to the first surface 14 of core
12, and a second cladding layer 18B applied to the second surface
16 of core 12. The core may be provided or prepared and may be a
sheet of material with the desired refractive index for the chosen
panel parameters. One important parameter is the acceptance angle
desired for light entering the panel. The core may have a thickness
of 10 mil, 20 mil, or any other thickness that will work in the
manufacturing process and result in a panel with the desired
acceptance angle and other screen characteristics. The cladding
layer may be about 0.1 .mu.m to 25 .mu.m thick. In one embodiment,
cladding layers 18A, 18B may include a light absorbing material.
The light absorbing material may be any suitable light absorbing
material, such as carbon black, a pigment, or a dye. The light
absorbing material may be a powder or a liquid dispersion.
[0017] FIGS. 5 and 6 show that waveguides 8 may further include a
light absorbing composition 19. Light absorbing composition 19
includes a light absorbing material such as carbon black, a pigment
or a dye. In one embodiment, light absorbing composition 19 may
form a single light absorbing layer on the first cladding layer
18A, as shown in FIG. 5. In another embodiment, light absorbing
composition 19 may form two light absorbing layers where a first
light absorbing layer 19A is on the first cladding layer 18A and a
second light absorbing layer 19B is on the second cladding layer
18B, as shown in FIG. 6. In another embodiment, the light absorbing
composition 19 may include an adhesive polymer.
[0018] As shown in FIGS. 7 and 8, waveguides 8 may further include
a layer of an adhesive composition 15 to adhere or bond adjacent
stacked waveguides together in forming the optical display panel.
In one embodiment, adhesive composition 15 may form a single
adhesive layer on the first light absorbing layer 19A, as shown in
FIG. 7. In another embodiment, adhesive composition 15 may form two
adhesive layers where one adhesive layer is on the first light
absorbing layer 19A and a second adhesive layer is on the second
light absorbing layer 19B, as shown in FIG. 8.
[0019] FIGS. 9 and 10 show waveguides 8 having an adhesive layer 15
applied to the first cladding layer 18A or the first and second
cladding layers 18A, 18B without a light absorbing layer in
between. In one embodiment, the adhesive layer 15 may include a
light absorbing material.
[0020] In another embodiment as illustrated in FIG. 11, a dichroic
filter 26 may be positioned between the back face 22 and the
reflector 29. The dichroic filter 26 may be selected to
substantially only pass light with the red, green and blue
wavelengths present in the image light from the projector. Since
most projectors project images with discrete wavelength red, green,
and blue light, using a dichroic filter 26 with pass bands at these
wavelengths will eliminate unwanted ambient light with out-of-band
wavelengths. Further, for projectors with laser or LED light
sources whose emitted image light exists in narrow bands, the
dichroic filter 26 would eliminate a substantial amount (if not
all) of out-of-band light. When ambient light enters the waveguides
from the front face 21, then the only ambient light reflected back
out the diffuser 24 (i.e. if any) would be ambient light that has
the same wavelengths as the projected image light. All other
ambient light will be blocked by the dichroic filter 26. Multiple
dichroic filter 26 layers may optionally be employed each having
suitable pass bands. For example, preferably each dichroic filter
26 will have a specific pass band corresponding to the red, green,
and blue light, respectively. Alternatively, in embodiments using a
back diffuser 24B, the back diffuser 24B may be placed either
between the back face 22 and the dichroic filter 26, or between the
dichroic filter 26 and the reflector 29. Two back diffusers may
alternatively be utilized, one placed between the back face 22 and
the dichroic filter 26, and the other placed between the dichroic
filter 26 and the reflector 29.
[0021] The optical core may be any optical grade material deemed
suitable for optical waveguides. For example, the optical core may
include one or more of the following: polycarbonates,
polymethylmethacrylate (PMMA), glass, polyesters, cellulose, cyclic
olefins and/or copolymers thereof, or other suitable optical grade
materials. The optical core may be one of the materials listed in
Table 1 above or combinations thereof. Examples of the polyester
cores include polyethylene terephthalate, polyethylene naphthalate
or a combination thereof. Cores are selected that have excellent
optical properties and will transmit light with minimal distortion
or absorption of light. To provide good viewing characteristics,
the optical core may have a percent transmission of between about
80 to about 100%. Transmissions less than 80 % may absorb or
scatter more light, thereby reducing the overall brightness of the
resulting waveguide.
[0022] In one embodiment the selected optical core may have a
refractive index between about 1.4 to about 1.6. A polycarbonate
core may have a refractive index of about 1.58. A PMMA core may
have a refractive index of about 1.48. A cellulose core may have a
refractive index of about 1.54. A polyethylene terephthalate core
may have a refractive index of about 1.57.
[0023] The cladding layers of the various waveguide embodiments
disclosed herein include a cladding material. The cladding material
may be any material having an index of refraction that is lower
than the index of refraction of the optical core. In one
embodiment, the cladding material may be a polyurethane, clear coat
containing dyes, silicones, cyanoacrylates, low index refraction
epoxies, plastics, or combinations thereof. In another embodiment,
the cladding material may be any polymer or polymer mixture that
has an index of refraction that is lower than the index of
refraction of the optical core and will result in a waveguide with
the desired acceptance angle range. Representative examples of the
cladding material include a butadiene, a polyester, a polyvinyl
pyrrolidone, an acrylic polymer or copolymer, a polyethylene oxide,
a polyvinylalcohol, an epoxy resin, an acrylate, an acrylate ester,
or combinations thereof. In one embodiment, the waveguide may have
an acceptance angle of .+-.5 to .+-.40.degree.. In another
embodiment, the waveguide may be designed to have an acceptance
angle of .+-.5 to .+-.30.degree..
[0024] Below are examples of various cladding material, however,
the cladding material is not to be construed as limited thereto. In
one embodiment, the butadiene may be a styrene butadiene, a
carboxylated styrene butadiene or combinations thereof available
from Dow Reichhold Specialty Latex or Mallard Creek Polymers. In
another embodiment, the polyester may be an anionic liquid
polyester available from EvCo Research LLC. Polyvinyl pyrrolidone
may be available from BASF. In one embodiment, the acrylic polymer,
copolymer, or latex may be a styrene acrylic, vinyl acrylic, or
carboxylated acrylic or mixtures thereof. The acrylic polymer,
copolymer, or latex may be available from Ciba Specialty Chemicals,
Dow Reichhold Specialty Latex, Para-Chem, or Specialty Polymers,
Inc. Polyethylene oxide may be available from The Dow Chemical
Company. Polyvinyl alcohol may be available from Dupont. The epoxy
resin may be a dispersion that may be available from Chemtrec or an
epoxy modified alkyl resin from Surface Specialties. The acrylate
may be n-butylacrylate latex, polyethylene glycol diacrylate,
carboxylated styrene acrylate, or other acrylates available from
Sartomer Company or Dow Reichhold Specialty Latex. Acrylate esters
may be available from Sartomer Company.
[0025] In one embodiment, the core selected is a polycarbonate
core, and the cladding material selected for use with the
polycarbonate core is a polystyrene butadiene available from
Mallard Creek Polymers. In another embodiment, the core selected is
a PMMA, and the cladding material selected for use with the PMMA is
a vinyl acrylic or a carboxylated acrylic copolymer or mixtures
thereof, available from Ciba Specialty Chemicals. In one embodiment
the cladding material is a mixture of carboxylated acrylic
copolymers, Glascol.RTM. RP4 and Glascol.RTM. RP3 microemulsions
that may be crosslinked by their carboxylic functionality. The RP3
and RP4 may be mixed as about 25% RP3 with about 75% RP4 to about
75% RP3 to about 25% RP4.
[0026] The cladding may include a surfactant. The surfactant is
usually added to the coating composition forming the cladding to
aid in the application of the cladding composition onto the core.
The surfactant helps the cladding composition flow smoothly during
manufacturing. The cladding composition may also include water. The
resulting cladding composition may be a mixture of liquids to form
a solution that may be mixed and used in the manufacturing
process.
[0027] Examples of surfactants include anionic surfactants,
amphoteric surfactants, cationic surfactants, and non-ionic
surfactants. Examples of anionic surfactants include
alkylsulfocarboxylates, alpha olefin sulfonates, polyoxyethylene
alkyl ether acetates, N-acylaminoacids and salts thereof,
N-acylmethyltaurine salts, alkylsulphates, polyoxyalkylether
sulphates, polyoxyalkylether phosphates, rosin soap, castor oil
sulphate, lauryl alcohol sulphate, alkyl phenol phosphates, alkyl
phosphates, alkyl allyl sulfonates, diethylsulfosuccinates,
diethylhexylsulfosuccinates, dioctylsulfosuccinates and the like.
Examples of the cationic surfactants include 2-vinylpyridine
derivatives and poly-4-vinylpyridine derivatives. Examples of the
amphoteric surfactants include lauryl dimethyl aminoacetic acid
betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium
betaine, propyldimethylaminoacetic acid betaine, polyoctyl
polyaminoethyl glycine, and imidazoline derivatives.
[0028] Examples of non-ionic surfactants include non-ionic
fluorinated surfactants and non-ionic hydrocarbon surfactants.
Examples of non-ionic hydrocarbon surfactants include ethers, such
as polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl
ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl
allyl ethers, polyoxyethylene oleyl ethers, polyoxyethylene lauryl
ethers, polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers;
esters, such as polyoxyethylene oleate, polyoxyethylene distearate,
sorbitan laurate, sorbitan monostearate, sorbitan monooleate,
sorbitan sesquioleate, polyoxyethylene monooleate, polyoxyethylene
stearate; glycol surfactants and the like. The above-mentioned
surfactants are typically added to the coating in an amount ranging
from about 0.1 to 1000 mg/m.sup.2, preferably from about 0.5 to 100
mg/m.sup.2.
[0029] The cladding may optionally further comprise one or more
conventional additives, such as biocides; pH controllers, matting
agents, preservatives; defoamers; viscosity modifiers; dispersing
agents; UV absorbing agents; anti-oxidants; and/or antistatic
agents. These additives may be selected from known compounds and
materials in accordance with the objects to be achieved. In one
embodiment, the above-mentioned additives may be added in a range
of 0 to 10% by weight, based on the solid content of layer.
[0030] The adhesive may be a rubber, a urethane, a cellulose
derivative, a polyester, a polyacrylate, an epoxide, a silicone, a
formaldehyde resin, a phenolic resin, a vinyl polymer, a polyether,
a furane, a polyaromatic, or mixtures thereof. In one embodiment,
the adhesive may be a dispersion. The dispersion may be aqueous or
in other solvent. In one embodiment, the adhesive may be a hot
melt. Examples of rubber based adhesives include natural rubber,
derivatives of natural rubber, synthetic rubber, or derivative of
synthetic rubber. The derivatives of synthetic rubber include
butyl, polyisobutylene, styrene butadiene, acrylonitrile
butadienes, neoprene, and chloroprene derivatives. Examples of
urethane based adhesive include polyurethanes, polycarboxylated
polyurethanes, and polyurethane polyesters. In one embodiment, the
urethane based adhesives may be aromatic or aliphatic. Various
urethanes may be available from CL Hauthaway & Sons Corporation
or Noveon, Inc. Examples of cellulose derivative based adhesives
include cellulose acetate, ethyl cellulose, and carboxy methyl
cellulose. The polyester based adhesive may be saturated or
unsaturated and examples thereof include polystyrene and
polyamides. Examples of polyacrylate based adhesives include
methacrylates, cyanoacrylates, and acrylamides. Examples of vinyl
polymer based adhesives include polyvinyl acetate, polyvinyl
acetal, and polyvinyl chloride. In one embodiment the adhesive may
be an aliphatic or aromatic polyurethane polyester adhesive. Such
adhesives may be an aqueous dispersion available from Cytec
Industries, Alfa Adhesives, Helmitin Inc., and Bayer
MaterialScience LLC.
[0031] In another embodiment, the adhesive composition may include
a thermosetting resin. The thermosetting resin may be an epoxy
resin selected from the group consisting of a biphenol epoxy,
urethane modified epoxy, a rubber modified epoxy and mixtures
thereof. In another embodiment, the thermosetting resin may be an
aqueous dispersion. Examples of thermosetting epoxy resins useful
in adhesive layer 20 are available from Resolution Performance
Products, such as EPR-REZ.TM. resin 5520--a urethane-modified epoxy
resin, EPR-REZ.TM. resin 3522--a solid Bisphenol A epoxy resin,
EPR-REZ.TM. resin 3540--a solid Bisphenol A epoxy resin with an
organic co-solvent, or EPR-REZ.TM. resin 3519--a
butadiene-acrylonitrile modified epoxy.
[0032] The light absorbing composition includes a light absorbing
material and an adhesive polymer. The light absorbing composition
forms a light absorbing layer as part of the various waveguide
embodiments described above and shown in FIGS. 1-8. The light
absorbing material may be any suitable light absorbing material,
such as carbon black, a dark material, a dark pigment, or a
dark-colored dye. Dark includes black, blue, or any other color
that is capable of absorbing ambient or other light entering the
waveguide at greater than the acceptance angle. Light entering the
waveguide or panel at greater than the acceptance angle needs to be
absorbed so it does not travel through the waveguide it entered in
to an adjacent waveguide, otherwise the image for the viewer may be
fuzzy. The light absorbing material may be a powder or a liquid
dispersion wherein particles to be dispersed are about 0.05 .mu.m
to about 20 .mu.m. In one embodiment the particles are about 0.05
.mu.m to about 7 .mu.m. In another embodiment the particles are
about 0.05 .mu.m to about 1 .mu.m. Carbon black may be obtained
from Cabot Corporation, Dick Blick Art Materials, Penn Color, Inc.,
Solution Dispersions, Inc., Wolstenholme International Ltd., or
Color Mate, Inc. In one embodiment, the light absorbing composition
may include carbon black and a binder, like an acrylic polymer, to
disperse the carbon particles.
[0033] A plurality of any of the embodiments of the waveguides 8
may be adhered together by positioning an adhesive layer 15 or a
light absorbing composition 19 including an adhesive between
stacked waveguides 8 and applying heat and/or pressure to the stack
to form a panel for use herein. The direction of the waveguides
within the front projection screens may be in a vertical or a
horizontal orientation, or any orientation therebetween.
[0034] Diffuser 24 may be any optical diffuser that alters the
angular divergence of incident light. Diffuser 24 may alter the
angle of divergence of incoming or outgoing light. The diffuser 24
provides a wider viewing angle for the audience viewing an image on
a front projection screen made of stacked waveguides. Diffuser 24
may be either a front diffuser 24A or a back diffuser 24B. In
another embodiment, both a front diffuser 24A and a back diffuser
24B may be present, as shown in FIG. 3.
[0035] In an embodiment including a front diffuser 24A, see Example
1 below, the front diffuser increased the brightness and image
sharpness, and eliminated or substantially reduced the reflection
hot spot in comparison to the same panel 20 without a diffuser. A
reflective hot spot is an area or spot which gives unusual high
reflective bright light across the screen surface. The hot spot may
be an enlarged and/or greatly blurred reflection of bright light.
The unusual brightness of the hot spot may obstruct the view of the
image by distorting the contrast with portion of the image
surrounding the hot spot. The viewer may be "blinded" by the hot
spot such that the rest of the image appears blurry. The panel
including the front diffuser 24A also had better brightness, black
density, and image sharpness than a conventional projection screen.
Films useful as the diffuser 24 may be available under the trade
name Illuminex from GE Advanced Materials, Diffusion Films or
Advanced Diffusion Films from Fusion Optixs, Inc., Opalus from
Keiwa Inc. of Japan, and Light Shaping Diffusers.RTM. from Luminit,
LLC. In one embodiment, diffuser 24 may be adhered or laminated to
the front surface 21 of the stacked waveguides 8 with an optical
adhesive, such as an optical grade acrylic, silicone, epoxy,
polyurethane or rubber based adhesive, or combination thereof. In
another embodiment, diffuser 24A may be attached to front surface
21 by a tape, a staple, a fastener, any other form of attachment
that will securely hold the diffuser in place without interfering
with the image to be viewed on the resulting screen, or
combinations thereof.
[0036] In another embodiment, an anti-glare film or coating may be
applied to diffuser 24 to improve the image by reducing the glare
and/or surface reflectivity of the screen. In another embodiment,
an abrasion resistant coating or film may be applied to diffuser 24
to protect the screen from damage. In another embodiment, a film or
coating having both anti-glare and abrasion resistant
characteristics may be applied to or may be part of the diffuser
24. In one embodiment, the antiglare and/or abrasion resistant film
or coating may be applied to or may be part an incorporated part of
the front diffuser 24A. The film may be adhered or laminated to the
diffuser 24. An optical grade adhesive may be used, the adhesive
should not degrade the diffuser 24. The lamination process may be
any method known in the art suitable for bonding the film to the
diffuser 24 without degrading the diffuser. The coating may be any
coating that has anti-glare and/or abrasion resistance
characteristics. The coating may be applied by any method known in
the art suitable for applying the coating without damaging the
diffuser or the stacked optical waveguides. The coating selected
should not react with the materials making up the diffuser 24 nor
destroy the diffuser characteristics of diffuser 24. Examples of
anti-glare films that also have abrasion resistant characteristics
include CV02 film by FUJIFILM and DuPont.TM. Optilon.TM.
Anti-Reflective Film Coatings by DuPont.
[0037] Reflector 29 may be a metal-based material. The metal-based
material may be selected from the group consisting of aluminum or
aluminum compounds, silver or silver compounds, titanium or
titanium compounds, gold or gold compounds, mercury or mercury
compounds, barium or barium compounds, stainless steel, and
mixtures thereof. Reflector 29 may be in the form of a film,
mirror, paper, glass, paint, or other suitable medium for placement
of the reflective material at the back face 22 of the stacked
waveguides 8. In one embodiment the reflective material is a
metallized film including aluminum, silver, or a mixture thereof.
The metallized film may be placed behind or on the back face 22 of
the stacked waveguides 8 by vapor deposition or via an optical
adhesive. In one embodiment the metallized film may be sandwiched
between an optical grade polymer to protect the metal within the
metallized film from reacting with compounds in the air, i.e.
oxygen, nitrogen, sulfur, water vapor. The metallized film may be
protected by an overcoat of or laminated between a protective
material such as polyethylene terephthalate. In embodiments
utilizing a back diffuser 24B, the reflector 29 may be placed
behind or on the side of the back diffuser 24B opposite the back
face 22 of the stacked waveguides 8.
[0038] In another embodiment, reflector 29 may be a microporous
PTFE or polyester comprising polymeric sheet. Examples of
microporous PTFE or polyester comprising polymeric sheet includes
Gore.TM. DRP.RTM. Diffuse Reflector by W. L. Gore & Associates
and DuPont.TM. Optilon.TM. Advanced Composite Reflector by Dupont.
Reflector 29 in film form may be adhered to the back face 22 of
waveguides 8 with an optical adhesive or tape. In another
embodiment, the reflector 29 may be a photographic paper. In one
embodiment, the photographic paper may include titanium dioxide.
The photographic paper may be adhered to the back face 22 with an
optical adhesive or tape. In another embodiment, reflector 29 may
be a reflective paint or reflective coating that may be painted,
coated, or sprayed onto the back face 22. In one embodiment, the
reflective paint or reflective coating may be a substantially
white. In another embodiment, the reflective paint or coating may
be of any paint that includes reflective beads or fillers. In
another embodiment, reflector 29 may alternatively be of a type
such as reflector 19 in U.S. Pat. No. 6,535,674 issued to Veligdan.
The reflector 29 may be in the form of a light directing film such
as, for example, a transmissive right angle film such as, for
example, TRAF II.RTM. from the 3M Company.
[0039] In one embodiment, the reflector 29 may be a dichroic
mirror. The dichroic mirror may be on or behind the back face 22 of
the stacked waveguides 8. In another embodiment, a polarized film
be placed between the back face 22 of the stacked waveguides 8 and
the dichroic mirror. The dichroic mirror may be selected to reflect
particular colors (i.e., wavelengths) of light while allowing other
colors (i.e., wavelengths) of light to pass through. The dichroic
mirror may be selected to substantially reflect light with the red,
green and blue wavelengths present in the image light from the
projector, while allowing other wavelengths to pass through. Since
most projectors project images with discrete wavelength red, green,
and blue light, using a dichroic mirror with reflective bands at
these wavelengths will eliminate unwanted ambient light with
out-of-band wavelengths. Dichroic mirrors may be available from
Optical Coatings Japan of type blue, green or red reflecting
mirrors and from PerkinElmer under the trade name ViewLux.
[0040] The panels including the diffusers are a combination of
components (i.e., including the core, the cladding, the light
absorbing material, the adhesives, the reflective material, the
diffusers, and any other layers present between the above
components) that are properly selected to create a panel with an
acceptance angle of incident light that will minimize the
interference from ambient light, such that the ambient light is
absorbed by the light absorbing material within the waveguide. This
provides the advantage that the screen made from such a panel will
maintain high brightness, contrast and low glare under ambient and
other various lighting conditions.
EXAMPLES
Example 1
[0041] An optical display panel made from waveguides having a
polycarbonate core with a refractive index of 1.58 and a cladding
with a refractive index less than the refractive index of the core
was evaluated to determine the effect of adding a diffuser(s) to
the panel. The waveguides were stacked and adhered to one another
to form the panel. An aluminum front surface mirror was placed at
the back surface of the panel. When a diffuser was included on the
panel, an Illuminex brand diffuser from GE Advanced Materials was
used. The diffuser was laminated to the appropriate face of the
panel as indicated in TABLE 1 below. The resulting panels were
evaluated in comparison to a Da-lite conventional screen on a scale
of 1 to 5 (where 5 is the best).
TABLE-US-00001 TABLE 1 Da-Lite No Front Back Front & Back
Conventional Diffuser Diffuser Diffuser Diffuser Screen Viewing
Angle 1 3 1 4 5 Brightness 2 3.5 3.5 2 1 Black Density 3.5 3 3.5
3.5 1 Image Sharpness 1 3 3 3 1 Projection Bright yes no (good) yes
no no Reflective Hot Spot (not good) (not good) (good) (good) BEST
2nd BEST
[0042] The results show that the panel with a front diffuser only
performed the best overall with the highest brightness and no
reflective hot spot. The panel that included a front diffuser and a
back diffuser performed second best with no reflective hot spot and
the highest viewing angle, but lower brightness than the panel with
only the front diffuser. Front projection screens having only a
back diffuser, as shown by these results, have reflective hot spot
that are bad for the viewing image. It was an unexpected result
that adding the diffuser on the front would eliminate the
reflective hot spot present with the rear diffuser.
[0043] Those of ordinary skill in the art will recognize that
various modifications and variations may be made to the embodiments
described above without departing from the spirit and scope of the
present invention. It is therefore to be understood that the
present invention is not limited to the particular embodiments
disclosed above, but it is intended to cover such modifications and
variations as defined by the following claims.
* * * * *